Aluminum compatibility question.

[754]

I want to build a piece from two 6061 plates. Held apart by a spacer with a step on the end going into reamed hole in the 6061, then held with washer and bolt.
Originally this spacer was to be stainless, but I am now thinking 7075 instead.
I am thinking this should not cause seizing problems. The pieces won't be twisting against each other, once in place , but might be occasionally removed or changed to different lengths.
So my question I , will they stick or gall ?

[Rich Carlstedt]

I doubt it, They are dissimilar enough to not gall as long as you don't contentiously rotate them under heavy load.
I would not use any lube as that may allow the rotation to occur. You could also put a plain paper washer between the two pieces of 7075 and 6061 and that will prevent any galling

Rich

[old mart]

If there is no twisting present then oil would do no harm. Or use a little non setting gasket compound. When aircraft sub assemblies are put together a compound of some type is normally put in the joints to seal them from ingress of water which is the principle cause of corrosion which makes disassembly difficult.

[projectnut]

For many years the company I worked for built it's own food processing and packaging machinery. The choice of materials was almost always 316 stainless and 6061 aluminum. About the only time we used other materials was in machinery exposed to corrosive liquids (brine) or harsh chemical wash down environments.

[Tim The Grim]

The metals themselves would be compatible and shouldn’t have any propensity to gall. However, if this is an automotive application and would be exposed to road salt, I would put a coat of synthetic grease on both dissimilar mating surfaces to reduce potential oxidation or galvanic action that might cause seizure. I’ve seen a 6061 plate delaminate from galvanic activity and look like an old paperback book that sat in a puddle and then dried out. Unfortunately it was on my old 289 powered Land-Rover. Road salt was the villain. I was the Bozo that built it and let that happen.